#include<stdio.h>

int GetSum(int start,int end)
{
  int sum=0;
  for(int i=start;i<=end;i++)
  {
    sum+=i;
  }
  return sum;
}

int main()
{
  int sum;
  int start,end;
  scanf("%d%d", &start,&end);
  sum=GetSum(start,end);
  printf("%d\n",sum);
  return 0 ;
}

